The present invention relates to an angular contact ball bearing, and in particular to an angular contact ball bearing of a steering shaft of an automotive vehicle, said bearing comprising an inner bearing ring, an outer bearing ring and bearing balls arranged between the inner and outer bearing rings in rolling contact with raceways formed on the inner and outer bearing rings, the inner bearing ring being received by an elastic tolerance ring of a polymeric material, said bearing further comprising a means for forming an inseparable assembly.
Angular contact ball bearings of the pre-cited type, which are generally made by shaping without chip removal, support axial forces only in one direction and therefore have to be placed against a second bearing. These bearings are preferentially used as steering bearings because they have only a small moment of friction and a relatively high rigidity while being simple and economic to mount.
One such angular contact ball bearing of the pre-cited type as frequently used for the mounting of steering shafts is known from DE 38 08 556 A1. The inner ring of this bearing is received by a plastic tolerance ring which engages around the inner and outer rings by a radial projection. At the other axial end of the inner ring, there is arranged a spring element in the form of a spring washer that is retained in the tolerance ring by a locking washer that is likewise secured in the tolerance ring by a radially inward directed projection. In this way, a pre-stressed assembly is formed out of the rolling bearing and the retaining and tensioning elements. Thus, a pre-assembled component is obtained that has only to be slipped-on in axial direction during mounting.
A drawback of the above construction is that, as viewed in axial direction, the tolerance ring extends over the entire length of the raceways of the bearing balls. This increases the overall radial dimension of the bearing because such a tolerance ring is made by injection and therefore must have a cross-section of  greater than 1 mm in its thinnest region.
It is an object of the invention to provide a steering bearing which eliminates the drawbacks of the prior art.
This and other objects and advantages of the invention will become obvious from the following detailed description.
The invention achieves the above objects by the fact that a retaining ring is arranged between the steering shaft and the tolerance ring, the retaining ring comprises circumferentially equi-spaced retaining elements that project therefrom in axial direction and comprise radially outward directed retaining lugs that overlap the outer bearing ring, the tolerance ring comprises circumferentially equi-spaced clearances for receiving the retaining elements, and the tolerance ring extends in axial direction up to the end of a generally radially extending portion of the inner bearing ring.
Due to the fact that the tolerance ring does not extend over the entire axial length of the bearing and further, that it comprises clearances for receiving the retaining elements, the bearing assembly of the invention has only a small overall radial dimension. The radial distance between the steering shaft and the inner bearing ring of the steering bearing is no longer determined, as it was hitherto, by the radial dimension of the tolerance ring in the raceway region but by the radial thickness of the retaining elements, but these can be made very thin, viz., in the region of some tenths of a millimeter. The retaining elements that overlap the outer bearing ring may have a resilient configuration, or they may be bent over outwards when mounting is completed. In both cases, the retaining lugs are instrumental in forming an inseparable assembly.
According to a further advantageous feature of the invention, the retaining ring comprises on an end opposing the retaining elements, at least one radially outward directed projection that engages into an associated recess in the tolerance ring. This radially outward directed projection serves as a mounting aid and thus facilitates the mounting of the bearing as a whole.
If such a bearing is used as an upper steering bearing in a longitudinal column, a means for transmitting electric current from the steering shaft through the rolling bearing to the steering tube must be provided. This is required for operating the signal horn or for releasing the airbag. Therefore, according to another feature of the invention, the conducting connection between the steering shaft and the steering tube is established through the retaining ring which, in accordance with the invention, is made of a material with good electric conductivity, for example copper or a copper alloy. In this case, it is particularly advantageous if the retaining elements comprise tabs pointing in both circumferential directions. If necessary, these tabs can then be folded over radially inwards so that a connection with good conducting properties is established between the retaining ring and the steering shaft.
According to another feature of the invention, the conducting connection between the steering shaft and the steering tube can be obtained by making the tolerance ring of a polymeric material that can conduct electric current. In this case, the electric conductivity of the polymer must be raised to match that of a metal. This can be achieved, for example, by adding carbon or steel fibers or soot particles to the polymeric material. This has the advantage that the conductivity of the polymeric material already exists during the fabrication process so that an after-treatment of the finished plastic component is not required. The conductivity of the polymeric material can, however, also be established by a metallic coating that may be deposited by galvanic, chemical or PVD methods. Galvanic methods require a conducting layer to be deposited on the plastic after this has been cleaned and roughened. With the galvanic technology it is basically possible to provide components of almost any shape with dense, pore-free and strongly adhering metal coatings. Deposition is effected in a known manner from watery solutions that contain the metal to be deposited in the form of ions. By an application of electric tension, the metal ions are transported to the surface of the component where they are reduced and settle down on the surface under adhesion. In chemical or currentless metallizing, as known, metal ions are precipitated from a salt solution by reducing agents. The metallic precipitate thus formed settles down on the plastic component. The metal layers deposited by direct, currentless metallizing are, however, generally very thin, their normal layer thicknesses lying in the range of 1 to 5 xcexcm. By PVD methods, a person skilled in the art understands coating methods based on the principle of xe2x80x9cPhysical Vapor Depositionxe2x80x9d i.e., the coatings are produced by the precipitation of atoms or molecules out of the gaseous phase. The thickness of these coating layers can range from some tenths of a xcexcm to some mm. PVD methods include vacuum metallizing, sputtering and ion plating.
According to still another feature of the invention, the angular contact ball bearing is biased in axial direction by an ondular washer which comprises circumferentially equi-spaced axial projections that engage into corresponding recesses of the tolerance ring. The ondular washer is thus connected in a detachable manner to the bearing assembly.
Finally, according to a last feature of the invention, the generally axially extending portion of the raceway of the outer bearing ring is followed by a step in the raceway which continues into an axial region of larger diameter that extends in axial direction up to the tolerance ring and ends in a radially outward directed flange. This division of the outer bearing ring by the step into two parts has a double advantage.
Firstly, when the bearing outer ring is fabricated by drawing, the tool for making the outer bearing ring can be matched separately to the shape of the raceway of the bearing balls and to the axially extending portion of the outer bearing ring. This has the positive effect on the bearing that any desired osculation can be achieved without regard to the axially extending region, i.e. independently of the outer diameter. Secondly, there is no negative effect on the raceway of the bearing balls when the angular contact ball bearing is pressed into the stationary steering tube with large tolerances because pressing-in is effected only with the axially extending portion of larger diameter. This assures a high basic load rating of the angular contact ball bearing.
The invention will now be described more closely with reference to the example of embodiment illustrated in the appended drawings.